Electrical characterization of n-channel MOSFETs with oxynitride gate dielectric formed by low-pressure Rapid Thermal Chemical Vapor Deposition

This study reports on n-channel MOS transistors using very thin oxynitride gate dielectrics deposited by Low-Pressure Rapid Thermal Chemical Vapor Dep osition (LPRTCVD). The threshold voltage, the transconductance, the fast an d slow trap densities, the low field mobility and its reduction factors hav e been investigated as a function of the nitrogen concentration in the film : The threshold voltage was found to decrease linearly with the nitrogen co ncentration, primarily because of the increase of the positive insulator ch arge density. At the same time, it has been shown that the quadratic mobili ty reduction factor is lower for a LPRTCVD oxynitride land nearly constant with the nitrogen concentration) in comparison to a thermal oxide. From thi s high field mobility attenuation, a lower transconductance is then expecte d for oxynitride-based transistors. Finally, we have shown that the presenc e of nitrogen in the oxide seems to induce more donor than acceptor traps a t the oxynitride-silicon interface.